检查另一个表中是否存在外键值？

Question

I wanna check whether a foreign key value exists in another table. What I'm trying to do is: I have a table named Gallery and another one named Posts . Posts is the parent table, so Gallery bears the post_id foreign key. On the posts.php page, since not every post has a gallery, I wanted to show a msg for each row, as in "has a gallery" or "does not have a gallery". For instance: post id 5 has a gallery and so does post number 10, but post id 1 doesn't have a gallery nor does post id 3. I'm thinking of a way like: Gallery table, if a gallery_id row has a 'null' value on column post_id, then echo "does not have a gallery." Else echo "has a gallery" if a gallery_id row has a 'null' value on column post_id, then echo "does not have a gallery." Else echo "has a gallery" , on posts.php . Is there a way of checking if a certain value exists in another table?

SQL code:

CREATE TABLE `gallery` (
 `gallery_id` int(11) NOT NULL AUTO_INCREMENT,
 `picture` varchar(200) NOT NULL,
 `post_id` int(11) NOT NULL,
 `gallery_date` datetime NOT NULL,
 PRIMARY KEY (`gallery_id`),
 KEY `post_id` (`post_id`),
 CONSTRAINT `gallery_ibfk_1` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=48 DEFAULT CHARSET=utf8mb4

I just tried

<?php
    $checkGallery = new Read();      
    $checkGallery->performQuery('gallery', "WHERE post_id = :post_id", "id_post={$post_id}");      
    if($checkGallery->result()):        
      $affirmative = $checkGallery->result(); 
?>

and then

<td class="values">
  <?= (  $affirmative ? 'This post has a gallery!' : 'No gallery enrolled in this post' );?> 
</td> 

Got no satisfactory results. It omitted certain rows instead of echoing "No gallery enrolled in this post"

Answer 1

Boom. I got it.

I just performed a query " SELECT * FROM gallery WHERE id_post =:id_post " (considering we are calling the bindValue method on posts.php )and id_post = $id; ( So, SELECT * FROM gallery WHERE id_post = 5 or... WHERE id = 3 and so on and the results are store in the $checkGallery array.)

<?php
  if($checkGallery):
?>
    <td><?= This post has a gallery! ?></td>
<?php else: ?>
    <td><?= No gallery attached to this post.?></td>
<?php endif;?>

And each row returns either " this post has a gallery " or " No gallery attached to this post ", all dynamically. Thanks